Sound absorber with partitions forming meandering channels connected to resonance duct



July 13, 19 F. HAAG 3,194,341

SOUND ABSORBER WITH PARTITIONS FORMING MEANDERING CHANNELS CONNECTED TO RESONANCE DUCT Filed Jan. 20, 1964 FIG. 3

INVENTOR FR/M/Z M746 United States Patent SQUND ABSORBER WITH PARTHTIONS FORMING MEANDERIN G CHANNELS CONNECTED TO RESONANCE DUCT Franz Haag, Plochingen (Neckar), Germany, assignor to Junkers & Co. G.m.b.H., Wernau (N eckar), Germany Filed Jan. 20, 1964, Ser. No. 339,015

Claims priority, application Germany, Jan. 21, 1963,

19 Claims. (c1. 1s1 s0) The present invention relates to sound absorbers in general, and more particularly to a device which serves to reduce the noise generated by sound waves in internal combustion engines, pulse jet burners and other types of fuel burning apparatus.

It is an important object of my invention to provide a comparatively simple, compact and inexpensive but highly effective sound absorber for use in fuel burning apparatus.

Another object of the invention is to provide a sound absorber which is particularly suited for use in various types of pulse jet burners.

A further object of the invention is to provide a sound absorber which may be utilized as a muffler in automotive vehicles and similar conveyances which are driven by internal combustion engines.

An additional object of the invention is to provide a sound absorber for pulse jet burners which is especially suited for reducing the noise of sound waves which travel down the resonance ducts of such burners.

Still another object of the invention is to provide a pulse jet burner which embodies a sound absorber of the above outlined characteristics.

A concomitant object of the invention is to provide a sound absorber which is embodied in a pulse jet burner and a portion of which constitutes an extension of the resonance duct of the burner.

An additional object of the invention is to provide a sound absorber which is embodied in a pulse jet burner and a portion of which constitutes an extension of the takeoff pipe which receives combustion products from the resonance duct.

A further object of the invention is to provide a sound absorber which may be readily taken apart, wherein at least some component parts may be readily exchanged by perfabricated parts so'tha the remainder of the sound absorber may be reassembled and put to renewed use in a pulse jet burner or another fuel burning apparatus.

With the above objects in view, one feature of my invention resides in the provision of a sound absorber, particularly for use in connection with the resonance duct of a pulse jet burner or another fuel burning apparatus wherein a sound wave and a column of gases travel down the resonance duct when the apparatus is in use. The sound absorber is interposed between the resonance duct and the take-oif pipe and comprises a hollow tubular housing whose interior is divided into a pair of spaces by a hollow partition which is formed with a series of cells extending in parallelism with the axis of the housing and defining two meandering channels one of which communicates with the resonance duct via one of the spaces and the other of which communicates with the take-off pipe through the other space.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved sound absorber itself, however, both as to its construction and the mode of assembling the same, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of a specific embodiice ment with reference to the accompanying drawings, in which:

FIG. 1 is a schematic axial section through a pulse jet burner which is equipped with the sound absorber of my invention;

FIG. 2 is a transverse section through the sound absorber as seen in the direction of arrows from the line IIII of FIG. 1;

FIG. 3 is an axial section through the sound absorber as seen in the direction of arrows from the line HIIII of FIG. 2; and

FIG. 4 is an axial sectional view showing a portion of a modified sound absorber in accordance with my invention.

Referring to FIG. 1, there is shown a fuel burning apparatus in the form of a pulse jet burner 10 including a combustion chamber 10a, a suction duct 10b which delivers to the chamber 10a a mixture of fuel and oxygen or oxygen-containing air, valves 10c, 10d which respectively control the admission of oxygen and fuel to the suction duct 10b, and a resonance duct 11 which serves to provide a path for evacuation of gaseous combustion products from the chamber 10a. The column of combustion products travels up and down the resonance duct in directions indicated by a double-headed arrow 10e. The arrow 10 indicates the direction of inflow of a mixture of fuel and oxygen into the combustion chamber. Of course, the burner 10 is further equipped with a suitable igniter device (not shown) as well as with certain other control devices which regulate the flow of oxygen and fuel to the valves 10c, 10d, but the exact construction of such control devices forms no part of my invention especially since, and as will be pointed out hereinafter, the invention resides in an improved sound absorber 12 which can be put to use in other types of fuel burning apparatus. I

The sound absorber 12 serves to reduce the noise of sound waves which travel down the resonance duct 11 whenever the combustion of the mixture admitted into the chamber produces a stream of combustion products which travels down the resonance duct and which induces in the chamber partial vacuum in a manner well known in the art of pulse jet burners.

The sound absorber 12 comprises an outer housing or casing including a tubular (preferably cylindrical) mantle or shell 13, a bottom end wall 14 and a top end wall 15. The end walls 14, 15 are detachably secured preferably with clamps (not shown), to the respective ends of the shell 13 in a manner shown in FIGS. 2 and 3. The means which connect the end walls 14, 15 to the shell 13 comprise suitable sealing rings or packings which insure that the joints are fluid tight so that air cannot enter and that the products of combustion cannot escape from the housing excepting in a manner to be pointed out as this description proceeds. The connections between the end walls 14, 15 and the shell 13 are strong enough to withstand the pressures which develop when the sound absorber 12 is used in a pulse jet burner. As a rule, the connections will include straps, collars and/ or clamps of known design (not shown).

The interior of the housing is divided in two substantially semicylindrical spaces 12', 12" by an axially disposed hollow partition 12a which comprises two spaced parallel side walls 16, 17 and a series of transverse walls 18 extending between the side walls 16, 17 and serving to divide the space between these side walls into a series of elongated cells 21, 22, 23, 24, 25, 26, 27 of rectangular or substantially rectangular cross-sectional shape. The cells 21-27 are parallel with the axis of the shell 13. As best shown in the right-hand portion of FIG. 2, the side walls 16, 17 are preferably provided with longitudinally extending grooves which receive the respective marginal portions of the transverse walls 18 and which insure that the transverse walls remain in requisite positions but may be slid in the axial direction of the shell. Each side wall and/ or each transverse wall may consist of several layers of suitable metallic material. The walls 13 are simple strips of laminated material which may be readily inserted into or withdrawn from the corresponding grooves of the side walls 16, 17 when the aforesaid preferred construction is employed.

The median transverse wall 18a extends all the way between the end walls 14, but the axial length of the remaining transverse walls 18 is less than the axial length of the shell 13. The walls 18 which are located to the left of the median wall 13a, as viewed in FIGS. 1 and 2, are staggered with reference to each other in the axial direction of the shell 13 so that they together form a meandering channel indicated by the reference numeral 28. The Walls 18 which are located at the right-hand side of the median wall 13a are staggered in similar fashion so that they together define a second meandering channel 29. The channels 28, 29 are connected with each other through the intermediary of the space 12', the channel 23 communicates with the resonance duct 11 through an inlet opening provided in the shell 13, and the channel 29 communicates with the space 12 which in turn cornmunicates with a take-off pipe 34 through a discharge opening provided in the shell 13. The take-oif pipe serves to convey the combustion products to the atmosphere.

The channel 28 communicates with the space 12' through an outlet Bl which is provided in the side wall 16 substantially midway between the ends of this channel. As shown, the channel 28 includes four cells 21, 22, 23, 24 and the outlet 31 is located between the cells 22, 23. The second channel 29 includes the cells 25, 26, 27 and communicates with the space 12" through a second outlet 33 which is provided in the side wall 17 at the discharge end of the cell 27. The space 12 communicates with the channel 29 through a port 32 which is provided in the side wall 16 at the lower end of the cell 25 so that the combustion products discharged at 31 and entering at 32 must travel in the axial direction of the shell 1'13 prior to entering the channel 29. The port 32 is located at the intake end of the channel 29 and the outlet 33 is located at the discharge end of this channel. The channel as has a blind portion including the cells 23, 24 the latter of which is adjacent to the median transverse wall 18a.

The spaces 12, 12" respectively accommodate axially parallel conduits 35, 36 the former of which serves to convey combustion products from the outlet 31 toward the port 32 and the latter of which serves to convey products of combustion from the outlet 33 toward the takeoff pipe 34. The conduits 35, 36 are provided with apertures 53 so that some of the conveyed gases may escape into the remainder of the spaces 12', 12". The remainder of each of these spaces, save for the portions adjacent to the end walls 14, 15, is filled with a suitable sound absorbent material 41 which surrounds the conduits 35, 36 and is in turn surrounded by the walls 16, 17 and shell 13. The additional lower and upper end walls 51 and 59 define with the end walls 14, 15 four compartments 37, 38, 39, at so that the compartments 3'7, 38 constitute the end portions of the space 12 and the compartments 39, 4d constitute the end portions of the space 12". The outlets 31, 33 respectively communicate with the compartments 37, 39, the compartment 38 communicates with the port 32, and the compartment 40 communicates with the take-off pipe 34. The ends of the conduit 35 communicate with the compartments 37, 38 and the ends of the conduit 36 communicate with the compartments 39, 49. The gases escaping radially through the permeable walls of the conduit 35, 36 penetrate to some extent into the material 41 whereby this material absorbs at least some noise so that the sound wave accompanied by gases traveling toward the take-off duct 34 is hardly noticeable or, at least, is weakened sutficiently to allow for use of the pulse jet burner in a home or a similar establishment.

The first cell 2;. communicates with the discharge end of the resonance duct 11, and it can be stated that the channel 28 actually constitutes an extension of the resonance duct. In accordance with an invention which is disclosed in my copending application Serial No. 338,976 the length of the combined resonance duct ill, 28 is substantially equal to or a multiple of one-half of the wavelength on which the pulse jet burner operates. The arrangement is preferably such that the outlet 33. is located at the peak (antinode) of the half Wave and the crosssectional area of the outlet 31 is less than the cross-sectional area of one of the cells 21-24, i.e., less than the cross-sectional area of the combined resonance duct ll, 23. The channel 29 actually constitutes the first section of a composite take-off pipe whose second section is formed by the pipe 34.

The sound absorber of my invention operates as follows:

The sound waves accompanied by products of combustion which are discharged from the chamber The pulsate in the composite resonance duct 11, 28 in directions indicated by the arrows ltle and s2 whereby a stream of such gases flows through the outlet 31 (arrow 43) and into the compartment 3'7 to how into the upper end of the conduit 35 (arrow .4). The quantity of gases which fiow into the outlet 31 corresponds to the quantity of gases which are discharged from the chamber Mia on consecutive explosions of the mixture which is admitted through the suction duct 19b. The stream of combustion products then continues to flow through the conduit 35 and passes through the compartment (arrow 45) on its way through the port 32. and into the channel 29, i.e., first through the cell 25, then through the cells 26, 27 in that order (arrows 46, t?) and through the outlet 33 to enter the compartment 39 (arrow 48). From the compartment 39, the gas flows through the conduit 3&5, into the compartment 4%, and into the take-oft pipe 34 (arrow The material 41 which fills the major parts of the spaces 12', 12" serves to absorb noise, and the second channel 29 including the cells 2527 serves as an acoustic mass to contribute further to a reduction in noise. The take-off pipe 34 may discharge the combustion products into the atmosphere.

The sound absorber 12 may be used as a muflier in an automobile or 1n a similar conveyance to reduce the noise of sound waves accompanying the exhaust gases which are produced by an internal combustion engine. In accordance with another modification of my invention, the sound absorber may be used in other types of pulse jet burners, for example, in those wherein vibrations of the resonance duct are achieved with a value corresponding to one-fourth of the wave-length on which the burner operates. Thus, and if the outlet 31 is replaced by a lar er outlet 31 (shown in FIG. 4), so that the crosssectional area of the outlet 31' is greater than the crosssectional area of the cell 22, the pulsation at such an enlarged outlet will be interrupted and the cells 23, then merely serve as reflection elements in a manner known from the art of pulse jet burners. The provision of a sound absorber at the end of the resonance duct is of particular importance when the duct vibrates with onefourth of the wavelength on which the burner operates.

The composition of the material 41 may be made out of slag or mineral wool or the like.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent 1s:

1. In a fuel burning apparatus, in combination, a duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; take-off means; and a sound absorber disposed between said duct and said take-otf means and comprising a hollow housing and a hollow partitlon provided in and dividing the interior of said housing into a pair of spaces one of which communicates with said take-cit means, said partition defining a pair of elongated channels one of which communicates with the other of said spaces and with said duct and the other of whichcomrnunicates with each of said spaces so that products of combustion travelling from said duct to said take-off means pass through said one channel, said other space, said other channel and said one space.

25. In a fuel burning apparatus, in combination, a resonance duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; a take-oil? pipe for combustion products; and a sound absorber disposed between said resonance duct and said take-cit pipe and comprising a sealed hollow tubular housing and a hollow partition received in and disposed in an axial plane of said housing so as to divide the interior of said housing into a pair of spaces one of which communicates with take-off pipe, said partition defining a pair of meandering channels each comprising a plurality of elongated cells extending in the axial direction of said housing, one of said channels being in communication with said resonance duct and with the other of said spaces and the other channel being in communication with each of said spaces so that products of combustion travelling from said resonance duct to said take-oil pipe pass through said first channel, said other space, said other channel and said one space.

3. In a fuel burning apar-atus, in combination, a duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; take-oft means; and a sound absorber disposed between said duct and said take-oif means and comprising a hollow housing and a hollow partition provided in and dividing the interior of said housing into a pair of spaces one of which communicates with said take-off means, said partition defining a pair of elongated channels one of which communicates with the other of said spaces through an outlet provided in said pantion substantially midway between the ends of said one channel and with said duct and the other of which communicates with each of said spaces so that products of combustion travelling from said duct to said takeoff means pass through said one channel, said other space, said other channel and said one space.

4. In a fuel burning apparatus, in combination, a resonance duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; a takeoff pipe for combustion products; and a sound absorber disposed between said resonance duct and said take-oft pipe and comprising a sealed hollow tubular housing and a hollow partition received in and disposed in an axial plane of said housing so as to divide the interior of said housing into a pair of spaces one of which communicates with said take-cit pipe, said partition defining a pair of meandering channels each comprising a plurality of elongated cells extending in the axial direction of said housing, one of said channels being in communication with said resonance duct and with the other of said spaces and the'other channel having a first end in communication with said other space through a port provided in said partition and a second end in communication with said one space through an outlet provided in said partition so that products of combustion travelling from said resonance duct to said take-off pipe pass through said first channel, said other space, said other channel and said one space.

5. In a fuel burning apparatus, in combination, a resonance duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; a take-oil pipe for combustion products; and a sound absorber disposed between said resonance duct and said take-off pipe and comprising a sealed hollow tubular housing and a hollow partition received in and disposed in an axial plane of said housing so as to divide the interior of said housing into a pair of spaces one of which communicates with said take-off pipe, said partition defining a :pair of meandering channels each comprising a plurality of elongated cells extending in the axial direction of said housing, one of said channels being in communication with said resonance duct and with the other of said spaces and the other channel being in communication with each of said spaces so that products of combustion travelling from said resonance duct to said take-off pipe pass through said first channel, said other space, said other channel and said one space, said partition comprising a pair of spaced substantially parallel side walls and plurality of transverse walls extending between said side walls to separate said channels and said cells from each other.

6. A combination as set forth in claim 5, wherein said side walls are provided with grooves extending in the :axial direction of said'housing and wherein said transverse walls have marginal portions which are receive-d in said grooves.

7. In a fuel burning apparatus, in combination, a resonance duct arranged to convey sound waves and gaseous products of combustion which develop, when the apparatus is in use; a take-off pipe for combustion products;

and a sound absorber disposed between said resonance duct and said take-cit pipe and comprising a housing ineluding a tubular shell having a first and a second end, a pair of end walls each arranged to seal one end of said shell, and connecting means .for detachably securing said end Walls to said shell, and a hollow partition received in and disposed in an axial plane of said housing so as to divide the interior of said housing into a pair of spaces one of which. communicates with said takeoff pipe, said partition defining a pair of meandering channels each comprising a plurality of elongated cells extending in the axial direction of said housing, one of said channels being in communication with said resonance duct through an inlet opening provided in said shell and with the other of said spaces through an outlet provided in'said partition and the other channel being in communication with each of said spaces so that products of combustion travelling from said resonance duct to said take-off pipe pass through said first channel, said other space, said other channel and said one space. i

8. In a fuel burning apparatus, in combination, a resonance duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; a take-off pipe; vand a sound absorber disposed between said duct and said pipe, said sound absorber comprising a hollow housing, a hollow partition provided in and dividing the interior of said housing into a pair of spaces one of which communicates with said pipe, said partition defining a pair of elongated channels one of which communicates with said resonance duct through an inlet opening provided in said housing and with the other of said spaces through an outlet provided in said partition and the other of which communicates with each of said spaces so that the products of combustion flowing from said duct to said pipe pass through said one channel, through said other space, through said other channel and through said one space, the cross sectional area of said outlet being less than the cross-sectional area of said one channel.

9. In a fuel burning apparatus, in combination, a resonance duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; a take-oil" .pipe; and a sound absorber disposed between said duct and said pipe, said sound absorber comprising a hollow housing, a hollow partition provided in and dividing the interior of said housing into a pair of spaces one of which communicates with said pipe, said partition defining a pair of elongated channels one of which communicates with said resonance duct through an inlet opening provided in said housing and with the other of said spaces through an outlet provided in said partition and the other of which communicates with each of said spaces so that the products of combustion flowing from said duct to said pipe pass through said one channel, through said other space, through said other channel and through said one space, the cross-sectional area of said outlet being greater than the crosssectional area of said one channel.

it). In a fuel burning apparatus, in combination, a duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; a take-off pipe for combustion products; and a sound absorber disposed between said duct and said pipe and comprising a sealed tubular housing, a hollow partition received in and disposed in an axial plane of said housing so as to divide the interior of the housing into a pair of spaces, said partition defining a pair of elongated meandering channels each comprising a plurality of elongated cells extending substantially in the axial direction of said housing, a first gas-permeable conduit provided in one of said spaces and extending substantially in the axial direction of said housing and a second gas-permeable conduit provided in the other space and extending substantially in the axial direction of said housing, one of said channels communicating with said duct through an inlet opening provided in said housing and with one end of said first conduit through a first outlet provided in said partition, and the other channel communicating with the other end of said first conduit through a port provided in said partition and with one end of said second conduit through a second outlet provided in said partition, the other end of said second conduit communicating with said pipe through a discharge opening provided in said housing so that products of combustion travelling from said duct to said pipe pass through said first channel, said first conduit, said second channel, and said second conduit.

ill. In a fuel burning apparatus, in combination, a duct arranged to convey sound waves and gaseous products of combustion which develop when the apparatus is in use; a take-off pipe for combustion products; and a sound absorber disposed between said duct and said pipe and comprising a sealed tubular housing, a hollow partition received in and disposed in an axial plane of said housing so as to divide the interior of the housing into a pair of spaces, said partition defining a pair of elongated meandering channels each comprising a plurality of elongated cells extending substantially in the axial direction of said housing, a first gas-permeable conduit provided in one of said spaces and extending substantially in the axial direction of said housing, a second gas-permeable conduit provided in the other space and extending substantially in the axial direction of said housing, one of said channels communicating with said duct through an inlet opening provided in said housing and with one end of said first conduit through a first outlet provided in said partition, and the other channel communicating with the other end of said first conduit through a port provided in said partition and with one end of said second conduit through a second outlet provided in said partition, the other end of said second conduit communicating with said pipe through a discharge opening provided in said housing so that products of combustion travelling from said duct to said pipe pass through said first channel, said first conduit, said second channel and said second conduit, and a body of sound absorbent material provided in and substantially filling the remainder of each of said spaces.

12. A combination as set forth in claim 11, wherein said sound absorbent material surrounds said conduits and wherein the axial length of said conduits is less than the axial length of said housing, said material and said housing defining between themselves four compartments each of which is disposed at one axial end of each of said conduits so that the products of combustion entering and leaving said conduits travel through said compartments.

13. As a novel article of manufacture, particularly for use in pulse jet burners and similar fuel burning apparatus, a sound absorber comprising a sealed hollow tubular housing having an inlet opening and a discharge opening; and a partition received in and extending in an axial plane of said housing so as to divide the interior of the housing into a pair of spaces one of which communicates with said discharge opening, said partition defining a pair of meandering channels each comprising a plurality of elongated cells extending substantially in the axial direction of said housing, one of said channels communicating with said inlet opening and with the other of said spaces through a first outlet provided in said partition and the other of said channels communicating with said other space through a port provided in said partition and with said one space through a second outlet provided in said partition.

14. As a novel article of manufacture, particularly for use in pulse jet burners and similar fuel burning apparatus, a sound absorber comprising a sealed hollow tubular housing having an inlet opening and a discharge opening; a partition received in and extending in an axial plane of said housing so as to divide the interior of the housing into a pair of spaces one of which communicates with said discharge opening, said partition defining a pair of meandering channels each comprising a plurality of elon gated cells extending substantially in the axial direction of said housing; and an elongated gas-permeable conduit provided in each of said spaces, one of said channels communicating with said inlet opening and with one end of the conduit in the other of said spaces through a first outlet provided in said partition and the other of said channels communicating with the other end of the conduit in said other space through a port provided in said partition and with one end of the conduit in said one space through a second outlet provided in said partition, the other end of the conduit in said one space being in communicating with said discharge opening.

15. A sound absorber as set forth in claim 14, wherein said inlet opening communicates with one end of said one channel and wherein said first outlet is provided substantially midway between the ends of said one channel.

16. A sound absorber as set forth in claim 14, further comprising a body of sound absorbent material provided in and substantially filling the remainder of each of said spaces.

17. A sound absorber as set forth in claim 15, wherein said sound absorbent material surrounds said conduits and wherein the axial length of said conduits is less than the axial length of said housing, said material and said housing defining between themselves four compartments each of which is disposed at one axial end of one of said conduits.

1 3. A sound absorber as set forth in claim 14, wherein said housing comprises a cylindrical shell having a first and a second open end, a pair of end Walls each arranged to seal one end of said shell, and connecting means for detachably securing said end walls to said shell.

19. A sound absorber as set forth in claim 14, wherein said partition comprises a pair of substantially parallel but spaced side walls and a plurality of transverse walls extending between said side walls to separate said channels and said cells from each other, said side walls having elongated grooves and said transverse walls having marginal portions longitudinally slidably received in said grooves.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Williams 181-69 Van Hoorn 18170 X Peik 18154 X Heath 181-36.2 Johnson 181-60 X Sharp et a1. 181-47 10 FOREIGN PATENTS 109,785 2/40 Australia. 674,670 10/29 France. 1,243,325 8/60 France.

LEO SMILOW, Primary Examiner.

LEYLAND M. MARTIN, Examiner. 

1. IN A FUEL BURNING APPARAUTS, IN COMBINATION, A DUCT ARRANGED TO CONVEY SOUND WAVES AND GASEOUS PRODUCTS OF COMBUSTION WHICH DEVELOP WHEN THE APPARATUS IS IN USE; TAKE-OFF MEANS; AND A SOUND ABOSROBER DISPOSED BETWEEN SAID CUCT AND SAID TAKE-OFF MEANS AND COMPRISING A HOLLOW HOUSING AND A HOLLOW PARTITION PROVIDED IN AND DIVIDING THE INTERIOR OF SAID HOUSING INTO A PAIR OF SPACES ONE OF WHICH COMMUNICATES WITH SAID TAKE-OFF MEANS, SAID PARTITION DEFINING A PAIR OF ELONGATED CHANNELS ONE OF WHICH COMMUNICATES WITH THE OTHER OF SAID SPACES AND WHICH SAID DUCT AND THE OTHER OF WHICH COMMUNICATES WITH EACH OF SAID SPACES SO THAT PRODUCTS OF COMBUSTION TRAVELLING FROM SAID DUCT TO SAID TAKE-OFF MEANS PASS THROUGH SAID ONE CHANNEL, SAID OTHER SPACE, SAID OTHER CHANNEL AND SAID ONE SPACE. 